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Build your first API with Phoenix

7th June 2019

Phoenix is an Elixir framework oriented to highly performant and scalable web applications, but before continuing, we need to know what is Elixir.


Elixir is a functional language designed for scalable and maintainable applications since it runs inside of threads of execution called processes to exchange information via messages. Another of its benefits is the fault-tolerance, that’s the reason for the expression “things will go wrong” but to confront the failures, Elixir provides supervisors that restart parts of your app when things go bad, going back to a known initial state that is guaranteed to work.

After this introduction, we are ready to code our first API!

The first thing before starting is to install Elixir:

brew install elixir

Once installed Elixir, we can install Phoenix running the next command:

mix archive.install hex phx_new 1.4.0

Now, we can create a Phoenix project:

mix phx.new books_store
Note: If we just want to build an API, we can add the next flags --no-html --no-webpack to avoid all HTML views and webpack that is included by default but for now, it’s ok.

After command ends we already have the project created! so we can run next instructions:

- cd books_store
- mix ecto.create
- mix phx.server 

Note: We need to be sure that we have Postgres installed because is the Database engine loaded by default in Phoenix.

Ecto is a library to interact with databases, we can say “is like an ORM”, but the difference is that Elixir is not an Object-Oriented language.

If everything goes well, we can visit http://localhost:4000 to see the welcome page.

The next step is to build our first schema and the JSON endpoint, running next command:

mix phx.gen.json Books Book books title:string price:integer publisher:string edition:string code:string

WhereBooks is the context, Book is our schema, books is the name of the table in the database and finally the attributes, then we got something like this:

Phoenix added all, controller, schema, migrations, tests, and json views. So now, we are going to add the resource to our routes lib/books_store_web/router.ex:

scope "/api", BooksStoreWeb do
  pipe_through :api
  resources "/books", BookController, except: [:new, :edit]

and run the migrations to create the books table with all attributes:

mix ecto.migrate

This command will insert into the database the schema we defined previously:

defmodule BooksStore.Repo.Migrations.CreateBooks do
  use Ecto.Migration
  def change do
    create table(:books) do
      add :title, :string
      add :price, :integer
      add :publisher, :string
      add :edition, :string
      add :code, :string

Before test our endpoint we need insert some data, we gonna do that through the console:

iex -S mix (access to the debug console)
alias BooksStore.Books
Books.create_book(%{title: "Elixir for beginners", price: 23_000, publisher: "McGraw", edition: "1st", code: "HH23DY"})
Books.create_book(%{title: "Phoenix for beginners", price: 15_000, publisher: "McGraw", edition: "3rd", code: "AAR67I"})

Run the server mix phx.server and go to a REST Client like Postman or Insomnia, just to check our endpoints:

Also, we can test the CREATE, UPDATE, and DELETE, all those actions live in our books_controller.ex file.

This is just an introduction to the Phoenix framework, how can we create an API in an easy way. This is the Phoenix documentation for more references.

See you soon!

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